Furnace and method of controlling the draft therein



July 17, 1923- 1.461.819 W. M. DUNCAN FURNACE AND METHOD oF CONTRDLDTNG THE DRAFT THEREIN Filed Dec.

16. 1,920 2 Sheets-Sheet 1 III Mmmm

July 17, 1923 W. M. DUNCAN FURNACE AND METHOD OF CONTROLLING THE DRAFT THEREIN Filed Dec.

2 Sheets-Sheet 2 .Patented July 17, 1923.

y WILLIAM M. DUNCAN, OF ALTON, ILLINOIS.

Lttlit FUBNCE AND METHOD OF CONTROLLING THE DRAFT THEREIN.

Application led December 16, 1920. Serial No. 431,168.

To all 'whom it may concern:

Be it known that I, WILLIAM M. DUNCAN, a citizen of the United States ofpAmerica, a resident of` Alton, in the county of Madison, State of Illinois,'have invented certain new and useful Improvements in Furnaces and Methods of Controlling-the Draft Therein, of which the Yfollowing is a full, cle-ar, and exact description, reference beinghad to the accompanying drawings, forming a part of this specification. l

This invention relates to improvements in furnaces and methods of controlling the draft therein. One of the objects of the invention is to avoid undue chilling of the combustible gases in the combustion chamber of thefurnace. Another object is to avoid undesirable cooling of the apparatus to be heated in the furnace. A further object is to prevent natural draft from interfering with a predetermined forced draft. An important object of the .invention is to accomplish all of the foregoing results in a mechanical stoker equipped with an lendless traveling chain grate. Prior to this inven- I tion, endless chain grates have been open at the front, rear and bottom so that currents of air entering at the front portions and lower portions of the grate can escape freely at the rear of the grate and pass into the combustion chamber. It has been customary to 'separate the rear of the grate from the bridge wall ofthe furnace and to discharge ashes between the traveling grate and the bridge wall. This has resulted in cold air currents, Awhich pass through or around the rear portion of the grate and into the combustion chamber above the grate. According to the present invention, such air currents are diverted from the combustion chamber so as to avoid interference with the predetermined forced draft in the combustion chamber, at the same time avoiding undesirable chilling of the combustible gases in the combustion chamber, and likewise preventing the chilling of the boiler to be heated by the fire.

With'the foregoing and other objects in view, the invention comprises the novel construction, combination and arrangement of parts hereinafter more specifically described and illustrated in the accompanying drawings, wherein is shown the preferred embodiment of the invention. However, it is to be understood that the invention comprehends changes, variations and modificachain grate.

tions which come within the scope of the claims hereunto appended..

Fig. I is a longitudinal section of a furnace embodying the features of this invention, the front portion of the furnace being broken away. Fig. II is an enlarged detail View, showing the traveling chain grate and the bridge wall at the rear of the grate, the middle portion of the grate structure being broken away. l

To illustrate' the invention I have shown an endless chain grate A passing around -a rotary tube l at the rear of the grate. A..

rotary power v shaft 2, at the front of the grate, is provided with anysuitable number of toothed drive wheels 3 meshing with the 4 designates draft boxes surrounded by the endless chain grate, each draft box having an inlet 5 for the admission of a forced draft. Each b ox is open at the top` to provide for the discharge of the forced draft through'the fuel supporting portion of the chain grate. The fuel is supplied through a hopper 6, from which it is discharged' onto the top of 'the grate, and the power shaft 2 is rotated to carry the fuel toward the rear of the grate.

A frame 7 supports the grate, draft boxes 4 and hopper 6,. and this frame may be mounted on wheels 8. Stationary bars, or rails 9, are located below the grate to prevent sagging of the lower portion of the grate.

The upper portion of the grate forms the bottom wall of a combustion chamber B. As an illustration of an apparatus to be heated, I `have shown a boiler comprising a boiler barrel 10 and a group of water tubes 11 communicating therewith. To deflect the hot gases, as indicated by arrows in Fig. I, baffles or deilectors 12 are located at the group of tubes and a deflector 13 is located above the' tubes. To create an eductive draft in the combustion chamber, the prod# ucts 4of combustion may pass out through a smoke stack 14, but it is to be understood that, any other suitable means may be employed to create or increase the draft.

A bridge wall 15 is separated from thel rear end of the traveling grate to provide a space for the outgoing ashes, which drop from the rear of the grate and fall into an ash outlet16, below the grate. The bridge wall is' stepped forwardly over the-extreme rear end of the grate and provided with draft outlets 17 leading into a duct 18, which may extend from the bridge wall to the stack 14, the object being to create an eductive draft at the draft outlets 17 near the 12 and 13. The hot gases'are thus obstructed in the furnace, but the air currents drawn through the draft outlets 17 in the bridge wall 15 can escape freely through the duct 18 and into the stack 14, so the eductive draft at the outlets 17 is greater than the eductive draft in the combustion chamber. Further variations in the draft can be obtained by adjusting a damper 19 (Fig. 1) to obstruct the gases passing from the combustion chamber tothe stack 14. A damper 20 in the duct 18 can also be adjusted to vary the draft a't the outlets 17 in the bridge wall 15. It is to be understood that other suitable means could be employed to obtain a comparatively strong draft at the outlets 17, and that in the app-aratus I have shown Athe drafts can be regulated by adjusting the dampers 19 and 20.

In the preferred form of the invention, a predetermined forced draft is discharged from the draft boxes 4 and through lthe fuel supported on the grate. The spaces between the upper portions of the respective draft boxes are closed by bars 21, and the space between the rear draft box and the rotary tube 1 may be closed by an apron 22 (Fig. II) pivoted at 23 and having its free end in engagement with the periphery of said tube. The upper portion of the grate is thussealed to prevent the admission of excess draft therethrough.

In an apparatus of the type herein shown,

. the grate is separated from the bridge wall 15 to provide for the discharge of ashes, and cold air currents are usually permitted to pass through and below the lower portions of the grate, as indicated by arrows in Fig. II. Air currents are also ermitted to rise from the ash outlet 16. eretofore these cold air currents have passed through the space between the grate and bridge wall 15, so as to escape into the combustion chamber. Excess air delivered to the combustion chamber in this manner tends to chill the hot ases in the combustion chamber, and it Furthermore, such excess air does not pass through the fuel to be consumed and it is not desirable for combustion in the furnace.

According to the present invention, the air currents tending to escape through the thin hed of ashes on the rear of the grate, or through the space between the bridge wall 15 and the grate are, diverted from the combustion chamber and discharged through the draft outlets 17 in the bridge wall 15. As previously indicated, the draft in the duct 18 is preferably equal to or greater than the eductive draft in the combustion chamber, so the air currents rising at the rear of the grate willbe directed through the outlets 17 in the bridge wall 15, instead of being rmitted to pass through the combustion c amber. Y

I claim:

1. A furnace having a combustion chamber, a mechanical stoker comprising a traveling chain,v grate forming the bottom wall of said combustion chamber, said combustion chamber being provided with an outlet for products of combustion, a bridge wall located 'at the rear of said traveling chain grate and extending across the lower portion o f the combustion chamber, said bridge wallhaving an outlet for the draft rising at the rear of said grate, and a draft producer including means whereby the eductive draft at the last mentionedl draft outlet is caused 'to exceed the eductive draft in said combustion chamber.

2. A furnace having a combustion chamber, a mechanical Stoker comprising a traveling chain grate forming the bottom wall of said combustion chamber, draft boxes surrounded by said traveling chain grate, said draft boxes being open at the top to provide for the discharge of a forced draft through the upper portion .of said chain grate, the fuel supporting portion of said grate being otherwise sealed to prevent escape of draft therethrough, a bridge wall separated from the rear of said grate, an ash outlet being formed below the rear of the grate to receive the ashes dropping between said grate and bridge wall, said combustion chamber having an outlet for' products of combustion and said bridge wall bein provided with a draft outlet into whic the draftl rising at the rear of the grate isdiverted from said combustion chamber, and a draft producer includin means whereby the eductive draft at said draft outlet is caused to exceed the eductive draft in said combustion chamber.

3. A furnace having a combustion chamber provided with a traveling grate and an ash passageway wherein ashes are dropped from one end of the traveling grate, and means for preventing the transmission of air from the ash passageway to the combustion chamber, said means4 including an air duct wherein a draft is maintained to withdraw air from said ash passageway, and said air duct -being in free communication with said ash passageway.

4. A furnace having a combustion chamber provided with a traveling grate, a bridgev bustion chamber, and said bridge wall being provided with a draft outlet leading from said ash passagewayto said air conductor.

5. A furnace having a combustion chamber provided with a traveling grate and an ash passageway wherein ashes are dropped from one end of the traveling grate, means for transmitting a forced draft through the fuel-supporting portion of the traveling grate, and means for preventing the transmission of air from the ash passageway to the combustion chamber, said means including an air duct wherein a draft is maintained to withdraw air from said ash passageway, and said air duct being in ,free

communication with said ash passageway.

6. The herein described method which comprises forcing a draft through the fuel on a travelin chain grate and into a combustion lcham ver above the grate, discharging ashes from the traveling grate and into an ash passageway at the rear of the grate, and 'withdrawing air from said ash passageway so as to prevent the delivery of said air to the combustion chamber. i v

7 The herein described method which comprises forcing a draft through thefuel on 'an endless traveling chain grate and into a combustion chamber above the grate, discharging ashes from the rear of said traveling grate, preventing the escape of natural draft'through the fuel supporting portion of said grate, diverting the natural draft into a' draft 'outlet near the rear of said grate, andmantaining an eductive draft at said draft outlet in excess of the eductive draft in said combustion chamber.

In testimony that I claim the foregoing I hereunto aix my signature.

WILLIAM M. DUNCAN. 

